In response to the query regarding the distinction, I thought I knew the
answer, but I had to look around to find actual definitions. The Funk
and Wagnals Standard College Dictionary defines "cultivar" as "a
horticultural variety of plant or flower [CULTI(vated) and VAR(iety)].
The "Dictionary of Anthropology" (Winick, Greenwood Press:NY 1956) gives
"cultigen" as "A plant which is dependent upon man for its survival".
The distinction seems to be between plants which can be grown in
gardens or live wild, and those which can only survive when tended by
humans. To check up on this I looked for a discussion in the
literature, a quick look. David Wilson offers a discussion on the
difference between a "cultivated" plant vs a "domesticated" plant in
his book _The New Archaeology_ (Knopf, 1974-paperback) chapter 8
(paperback p.161). I hope this is what you were looking for.